When two user equipment terminals (e.g., mobile communication devices) of a cellular network or other telecommunication system communicate with each other, their data path typically goes through the operator network. The data path through the network may include base stations and/or gateways. If the devices are in close proximity with each other, their data path may be routed locally through a local base station. In general, communications between a network node such as a base station and a wireless terminal is known as “WAN” or “Cellular communication”.
It is also possible for two user equipment terminals in close proximity to each other to establish a direct link without the need to go through a base station. Telecommunications systems may use or enable device-to-device (“D2D”) communication, in which two or more user equipment terminals directly communicate with one another. In D2D communication, voice and data traffic (referred to herein as “communication signals”) from one user equipment terminal to one or more other user equipment terminals may not be communicated through a base station or other network control device of a telecommunication system. Device-to-device (D2D) communication has more recently also become known as “sidelink direct communication”.
D2D communication, e.g., sidelink direct communication, can be used in networks implemented according to any suitable telecommunications standard. A non-limiting example of such as standard is the 3rd Generation Partnership Project (“3GPP”) Long Term Evolution (“LTE”). The 3GPP standard is a collaboration agreement that aims to define globally applicable technical specifications and technical reports for third and fourth generation wireless communication systems. The 3GPP may define specifications for next generation mobile networks, systems, and devices. The 3GPP LTE is the name given to a project to improve the Universal Mobile Telecommunications System (“UMTS”) mobile phone or device standard to cope with future requirements. In one aspect, UMTS has been modified to provide support and specification for the Evolved Universal Terrestrial Radio Access (“E-UTRA”) and Evolved Universal Terrestrial Radio Access Network (“E-UTRAN”). E-UTRAN is another non-limiting example of a telecommunications standard with which D2D communication may be used. A non-exhaustive list of 3GPP documents which describe, at least in part, device-to-device (D2D) communication (e.g., “sidelink direct communication”) include the following (all of which are incorporated herein by reference in their entireties):    3GPP TS 36.201 v12.1.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); LTE Physical Layer; General Description (Release 12) (2014-12);    3GPP TS 36.211 v12.4.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 12) (2014-12);    3GPP TS 36.212 v12.3.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and Channel Coding (Release 12) (2014-12);    3GPP TS 36.213 v12.0.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer Procedures (Release 12) (2013-12);    3GPP TS 36.214 v12.1.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer; Measurements (Release 12) (2014-12);    3GPP TS 36.300 v12.4.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall Description; State 2 (Release 12) (2014-12);    3GPP TS 36.304 v12.3.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) Procedures in Idle Mode (Release 12) (2014-12);    3GPP TS 36.306 v12.3.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) Radio Access Capabilities (Release 12) (2014-12);    3GPP TS 36.321 v12.4.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) Protocol Specification (Release 12) (2014-12);    3GPP TS 36.322 v12.1.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) Protocol Specification (Release 12) (2014-9);    3GPP TS 36.323 v12.2.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Packet data Convergence Protocol (PDCP) Specification (Release 12) (2014-12); and    3GPP TS 36.331 v12.4.0, Technical Specification, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC) Protocol Specification (Release 12) (2014-12).    Device to device (D2D) communications provide proximity-based applications and services, representing an emerging social-technological trend. The introduction of a Proximity Services (ProSe) capability in LTE allows the 3GPP industry to serve this developing market, and, at the same time, serve the urgent needs of several Public Safety communities that are jointly committed to LTE. The current assumptions related to D2D communication is that a wireless terminal within network coverage uses resources for D2D discovery and communication assigned by the controlling node. If the wireless terminal is out of network coverage, it may use pre-assigned resources for communications. If the wireless terminal incorrectly determines its situation of in/out of network coverage, e.g., if the wireless terminal tries to use the pre-assigned resources within network coverage, it may affect the current LTE networks with strong interference and thereby be very dangerous. Therefore, a problem which needs to be solved for D2D communications is how the wireless terminal determines whether it is in or out of network coverage.
D2D services include ProSe Direct Communication (e.g., D2D communication, sidelink direct communication) and ProSe Direct Discovery (e.g., D2D discovery, sidelink direct discovery). ProSe Direct Communication is a mode of communication whereby two wireless terminals can communicate with each other directly over the PC5 interface (i.e., direct interface between two wireless terminals). This communication mode is supported when the wireless terminal is served by E-UTRAN and when the wireless terminal is outside of E-UTRA coverage. A transmitter wireless terminal transmits a Scheduling assignment (SA) to indicate the resources it is going to use for data transmission to the receiver wireless terminals. ProSe Direct Discovery is defined as the procedure used by the ProSe-enabled wireless terminal to discover other ProSe-enabled wireless terminal(s) in its proximity using E-UTRA direct radio signals via the PC5 interface.
Generally, the network coverage detection should be based on the downlink received power. In current 3GPP specification TS 36.213, Version 12.0.0, see http://www.3gpp.org/DynaReport/36213.htm, the downlink received power is measured with respect to cell-specific reference signal strength. The coverage can be defined by wireless terminal's downlink received power measurement, or be defined by wireless terminal's RRC state for simpler implementation and specification work. The downlink radio link quality of the primary cell is monitored by the wireless terminal for the purpose of indicating out-of-sync/in-sync status to higher layers. The physical layer in the wireless terminal shall, in radio frames where the radio link quality is assessed, indicate out-of-sync to higher layers through a radio link failure (RLF) report when the radio link quality is worse than the threshold Qout. When the radio link quality is better than the threshold Qin, the physical layer in the wireless terminal shall, in radio frames where the radio link quality is assessed, indicate in-sync to higher layers.
Reusing the out-of-sync definition for out-of-coverage detection in relation to D2D communication has several problems. For example, the RLF is only declared when the UE wireless terminal in RRC_CONNECTED mode. Furthermore, even the RLF is reported to be a correct out-of-coverage indication, it is for the primary cell only, i.e., the wireless terminal may still be in coverage of other usable networks in the same area.
A wireless terminal in Long Term Evolution (LTE) may be in one of two LTE radio resource control (RRC) states or modes: RRC_IDLE or RRC_CONNECTED. A wireless terminal is in RRC_CONNECTED when an RRC connection has been established. If this is not the case (i.e., if no RRC connection is established) the wireless terminal is in RRC_IDLE state. For RRC Idle mode wireless terminal, some metrics, such as the synchronization signal (SS) strength or broadcast signal strength, may be defined as measurement of out-of-coverage. However, these metrics are very complicated to be implemented in LTE networks. All of these bring new heavy burdens to legacy LTE networks.
For reasons mentioned above, in D2D communications when the D2D service and LTE cellular service share the same frequency band, the wireless terminal needs to behave correctly based on whether it is in or outside the coverage of network, so as to minimize its compact (interference) on the present networks, e.g., LTE networks. A problem in this area is to detect the network coverage accurately and efficiently, so that (among other reasons) the wireless terminal in device-to-device (D2D) communications will not interfere with network operation.
What is needed, therefore, among other things are methods, apparatus, and/or techniques for selecting resource utilization methods for purposes such as controlling behavior of a device-to-device (D2D) capable wireless terminal and detecting network coverage for purposes such as ascertaining whether a device-to-device (D2D) capable wireless terminal is in-coverage or out-of-coverage, such as (for example) when the wireless terminal is in Idle Mode. The methods, apparatus, and/or techniques provide benefits that reduce system complexity and improve communication flexibility and efficiency.
In D2D communications, if the D2D service and LTE cellular service share the same frequency, the resource allocation to UE needs to be performed correctly based on whether it is in or outside the coverage of network, so as to minimize its compact (interference) on the present networks, e.g., LTE networks. On the other hand, the issue of load balancing may also be pertinent for an in coverage scenario when one resource allocation method cannot have adequate resources for allocation while another method still has enough resources.
As the above mentioned resource allocation problem is closely related to the detection of coverage, the detection problem can easily be solved by methods associated with legacy LTE RRC states (in the agreements of 3GPP TSG RAN WG2 Meeting #85-bis), e.g., the UE is in coverage if it is in RRC_CONNECTED state. However, if the UE supports multi-carrier communications, the problem becomes more complicated. A complication may arise, for example, when one carrier of the UE is in RRC_CONNECTED mode, and another carrier has no RRC connection.